At least six people were dead and 31 missing after a tourist boat sank in a reservoir in northwestern Colombia on Sunday, June 25, the country's president said, according to AFP.

Authorities did not yet say what caused the four-deck Almirante to go down in the El Penol reservoir in the tourist town of Guatape, where Colombian and foreign tourists take leisure cruises.

There are "six people deceased so far and 31 reported missing," Santos told reporters in Guatape, after the regional government earlier gave a death toll of at least nine.

An official in the National Risk Management Unit, Carlos Ivan Marquez, confirmed the toll of six separately to AFP. He said they were "all Colombians, and no minors."

Regional authorities said the boat was carrying 170 people, most of whom were rescued by other boats or escaped by themselves.

"It sank extremely quickly. It all happened in a few minutes," said a fire service captain involved in the rescue effort, Luis Bernardo Morales.

One helicopter from the air force and two from the army went to help in rescue operations, the military said.

The reservoir is 68 kilometers (40 miles) from the city of Medellin and is one of Antioquia department's main tourist draws.